1993 BMW 850cilimp mode

Help!!
My name is Sandres and I live in MD. I own a 1993 BMW 850ci that started in and out limp mode
My mechanic has checked everything possible to find out why the car goes in and out of limp mode. He is currently checking to see if there is a short somewhere. Has anyone had this problem? If so please tell me what may be causing this problem.

I'm only getting limp mode. It goes off and work fine for a while and suddenly limp mode and lost of power. My mechanic has checked transmission, no problem; switched out and checked MAFs, no problem, crank sensors, no problem; checked coils, no problem; checked fuel pumps, no problem. One of the engine banks ( i'm not sure left or right) is not picking up a good signal from the ecu. He switched around both and checked, no problem. Now he's checking the wiring to see if there may be a problem there. A great German mechanic, he curses the car but refuse to give up until he finds the problem.